Just sitting here waiting for Emily's Cat, because she has chapter and verse on all this, due to having a relative who was directly affected by it.
It's been an incredibly busy week, and this thread has suddenly become a lot more active!
Alrighty then.
My godchild has Kallmann Syndrome, and is at the more extreme end of the possible impacts. While it's not a chromosomal disorder, it's still considered a Disorder of Sexual Development, because the condition interferes with how puberty proceeds. Puberty in humans is a two-part process, which involves the adrenal gland and the pituitary gland. In generalities, the adrenal governs the growth of the long bones, closure of the growth plates, and the development of fine armpit, pubic, and leg hair. The pituitary governs production of sex hormones, and during puberty it prompts development of secondary sex characteristics that differ by sex, as well as the accretion of bone density. The pituitary drives the hormone flood that in females results in widened hips, maturation of milk glands in the breast, deposition of fatty deposits in the breast, buttocks, and hips, enlargement of the uterus, and onset of menarche. In males, it drives an increase in muscle density, descent of the scrotum further away from the body, enlargement of the penis, coarsening of leg and arm hair, and the growth of facial hair.
Kallmann syndrome is a condition that affects the pituitary gland, but not the adrenal. In my godchild's case, their pituitary didn't trigger ANY of its pubertal function at all. This is a particular concern because a failure for the two glands to work in concert has deleterious effects. The most immediate of those is that the long bones grow but do not increase in density which makes them brittle. And if the growth plates close before accretion occurs, there's no way to reasonably address that brittleness. So you get a child that grows taller, but whose bones become weaker in the process. Additionally, without the pituitary side of the system functioning, the child becomes sterile. In females, eggs never mature and never begin being released; in males, the testes don't fully mature and don't begin producing sperm.
Puberty blockers ONLY block the production of sex hormones - thus they only impact the pituitary half of the process. They do not halt or slow down the adrenal process at all.